How family size affects your health: New study reveals surprising patterns

Parenthood exerts profound impacts on adult health. However, previous studies have largely focused on women and limited health outcomes, often producing inconsistent results due to variations in definitions of parenthood, insufficient adjustment for confounders, and short follow-up periods.

In this large-scale, population-based prospective cohort study, published in the Chinese Medical Journal on October 09, 2025, researchers used data from the China Kadoorie Biobank (CKB)—which includes over 500,000 adults aged 30–79 across 10 regions of China—to investigate the associations between the number of biological offspring (without vs. with offspring; more than one vs. one offspring) and a wide range of health conditions using a phenome-wide association study (PheWAS) approach. Analyses were performed separately for men and women. “Our study represents a major step forward because we looked at the relationship between the number of children an individual has and their health outcomes across the entire spectrum of human disease, a concept called ‘phenome-wide,’” shares Dr. Dianjianyi Sun from the School of Public Health at Peking University Health Science Center, one of the authors.

The study employed a rigorous, sex-stratified approach, primarily using PheWAS to systematically test the association between the number of offspring and a vast range of ICD-10 coded diseases. Cox Proportional-Hazards Models were used for the prospective analysis of morbidity and all-cause mortality over 12 years. The main exposure was analyzed through comparisons of childless individuals versus those with one offspring, and by modeling each additional offspring to quantify health risks. Finally, the Hazard Ratio (HR) was used as the statistical measure to represent the ratio of the instantaneous risk of an event occurring in an exposed group compared to the risk in an unexposed (reference) group, over a specified follow-up period. All resulting HRs were comprehensively adjusted for potential confounders to ensure the isolated effect of parity was measured.

After excluding diseases with fewer than 30 cases to ensure adequate statistical power, 568 diseases for men and 654 diseases for women were retained for PheWAS analysis. The PheWAS results, corrected for multiple testing using the Bonferroni method, revealed that having no biological offspring was strongly associated with an increased risk of schizophrenia in both men and women. Moreover, having more than one offspring compared to one was associated with disease risks across multiple systems.

Subsequent prospective analyses showed that, compared to men with one offspring, those without biological offspring had increased risks for nine of 36 diseases, including mental and behavioral disorders, cardiovascular disease, and respiratory conditions. Among women, those without offspring showed higher risks for five diseases of 37 diseases, including mental and behavioral disorders and cardiovascular conditions. Each additional offspring was associated with a 7% reduction in mental and behavioral disorders in both sexes, and an 18% lower breast cancer risk specifically in women. However, each additional offspring increased women's cholelithiasis and cholecystitis risk by 4%.

Meanwhile, among 282,630 patients with any of 26 self-reported diseases at baseline in CKB, 44,533 deaths were recorded. Interestingly, compared to those with offspring, male and female patients without offspring had a 37% and 27% higher risk of all-cause mortality, respectively. Additionally, among male patients, each additional offspring was associated with a 4% reduction in mortality risk. While among women, the lowest risk was observed among those with three to four offspring.

In summary, this study highlights a complex, sex-specific relationship between the number of biological offspring and long-term risks of morbidity and mortality in Chinese adults. Further research is needed to verify these findings, explore the underlying biological, behavioral, and social mechanisms involved, and elucidate potential causal relationships. Dr. Sun concludes, “We have demonstrated a robust, system-wide link between reproductive history and long-term health, highlighting the need for healthcare systems and policymakers to provide tailored health monitoring and support for individuals at both ends of the parity spectrum, to those who are childless, and to those who have larger families. This in turn can help address their specific, newly identified health vulnerabilities.”